A bi-directional chopper is a known example of a conventional power conversion device (for example, see Introduction to Power Electronics (English translation of Japanese title), edited by KAWAMURA Atsuo, Corona Publishing Co., Ltd., February, 2009, pp. 57-83 (NPL 1)). FIG. 10 is a circuit diagram of a conventional bi-directional chopper. The bi-directional chopper 2 converts DC voltage input from a DC power source in accordance with the ratio that a switching element 45 or 46 is on. In the case of using a step-down chopper, a DC power source is connected between terminals A and B, a load is connected between terminals C and D, the switching element 46 is always turned off, and the switching element 45 is subjected to switching control (on/off control). In this case, the output voltage is determined by the duty cycle (conduction ratio) of the switching element 45. On the other hand, in the case of using a step-up chopper, a load is connected between terminals A and B, a DC power source is connected between terminals C and D, the switching element 45 is always turned off, and the switching element 46 is subjected to switching control. In this case, the output voltage is determined by the duty cycle of the switching element 46.
In this bi-directional chopper 2, the power source voltage is applied to the switching element 46 when the switching element 45 is on, and the power source voltage is applied to the switching element 45 when the switching element 46 is on.
Furthermore, in the bi-directional chopper 2, the switching elements 45 and 46 can each be configured as two switching elements that are connected in series (for example, see JP 2010-124596 A (PTL 1)).